Fluorescent PH Sensor Based On Composite Quantum Dot Film

pH is one of the most important physical and chemical parameters of aqueous solutions,and it is also an important parameter of physiological activity,chemical reaction and water environment.In general,abnormal pH changes usually indicate the occurrence of diseases such as the production of a disease,the failure of a chemical reaction,or the pollution of a water environment.Therefore,pH monitoring has always been one of the core tasks in the fields of industrial production,biomedicine and environmental protection.Fluorescent pH sensors generally use surface-modified fluorescein molecules to work with pH-sensitive fluorescence characteristics.However,the stability and reusability of the performance are also challenged by defects such as leakage of fluorescein molecules and fluorescence quenching.Herein,we design a fluorescence pH sensor consists of three parts:LED excitation layer,quantum dot fluorescent layer and pH sensitive molecular probe layer.Commercial LEDs emitting wavelengths of 365-400 nm were selected as excitation layers,inorganic perovskite CsPbX3(X=Cl,Br,I)quantum dots and polymer composited thin film were selected as fluorescent layer,Bromothymol blue(BTB)combined with hydrogel HydroMed D4 to work as pH-sensitive molecular probe layer.The light of excitation layer is transmitted to the fluorescent layer,and the fluorescent layer is excited to emit fluorescence,which would be absorbed by the pH-sensitive probe molecule layer.The value of the pH can be reflected by the transmitted fluorescence signal.The main research contents and results of this article are as follows:1.Synthesis and Optical Properties of Inorganic Perovskite CsPbX3(X = Cl,Br,I)Quantum Dots.High-temperature organic phase method was used to prepare CsPbCI3,CsPbBr3 and CsPbI3 with the peaks of 407 nm,510 nm and 677 nm,respectively.Fluorescence CsPbX3 Quantum Dots with emission of 417-714 nm in the Visible Light Region were prepared by Ion Exchange Method.The effects of temperature and solvent on the optical properties of CsPbBr3 were studied.It was found that the higher the temperature,the lower the fluorescence efficiency of CsPbBr3 quantum dots at 0-800C.At the same concentration,the lower the polarity of the solvent,within which the CsPbBr3 quantum dots are dispersed,the better of dispersibility and the better of fluorescence performance.The n-hexane with a polarity of 0.06 can be used as a good solvent for the inorganic perovskite CsPbX3(X=Cl,Br,I)quantum dots.The fluorescence characteristics of CsPbI3 QDs containing I elements stored in air were also studied.It was found that fluorescence intensity gradually decreased and resulted in fluorescence quenching over the time.2.Preparation and Optical Properties of inorganic Perovskite CsPbX3(X=Cl,Br,I)Quantum Dots and Polymer Composite Films.The preparation and optical properties of CsPbX3(X=Cl,Br,I)QDs,poly(methyl methacrylate)(PMMA)composite films and polystyrene(PS)composite films were investigated.Both composite films have been found to have a certain degree of acid and alkali resistance,but PMMA has the effect of quenching the fluorescence quantum dots,especially the CsPbI3 quantum dots.However,PS has a good effect on the isolation of water and oxygen from quantum dots,which can achieve the protection of quantum dots.3.Study on the Optical Properties of Bromothymol Blue(BTB)and Hydrogel HydroMed D4 Composite Films in Different pH Buffers.It was found that when the concentration of BTB was 0.00325 mmol/L,the absorption intensity decreased with the increase of pH at 431 nm,and when the concentration was 0.49 ?mol/L,the absorption intensity of 617 nm increases with increasing of pH from 8 to 12.When the concentration of BTB in the composite thin film solution was 0.05 mmol/mL,the absorption intensity of 415 nm decreased with the increase of pH within the range of pH=3-7,and the concentration of BTB in the composite thin film solution was 0.01 mmol/L,the absorption intensity of 617 nm increases with pH from 8 to 11.4.Fluorescence pH Sensor Design and Fluorescence pH Sensor Characteristics and Testing.By studying the relationship between fluorescence signal changes and pH sensing,the sensor shows a segmented linear relationship between transmitted fluorescence singnal and buffers with pH=3-11.The result revealed that the sensor have the potential to detect the pH of solution.